This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 56 394.2, filed on Nov. 24, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method of manufacturing a shaped profile member of a hybrid composite material including a stack of alternating metal layers and fiber-reinforced composite layers.
Various methods of manufacturing profile members of a hybrid composite material including fiber-reinforced plastic composites and metals are generally known. Typically, such methods involve forming a stack of alternating layers of fiber-reinforced composite material and of metal sheets in a planar configuration and then curing or hardening the composite material layers in the flat planar configuration. After the flat planar stack of material has been cured and hardened, conventional forming processes are used to reform the flat planar hybrid stack into the desired finished, profiled or contoured configuration. The forming capabilities of such forming processes are limited in that they are able to achieve only relatively large radii of curvature by an plastic deformation of the laminated stack of hybrid materials. For that reason, the use of such methods for fabricating profile members for aircraft construction has found only limited application, and is not suitable for all possible uses or purposes in the construction of an aircraft.
Moreover, the initially flat planar laminated stack of hybrid metal and composite layers, which is then subjected to a forming process to achieve the required deformation, will exhibit a certain xe2x80x9cspring backxe2x80x9d deviation of the finished deformed contour back toward the original flat planar configuration. It is very difficult to predetermine and thus correct for, or to otherwise avoid, such contour deviations from the desired configuration, which result from the spring-back phenomenon. For this reason, it is extremely difficult to achieve a required finished contour with high precision using the conventional techniques.
It has further been found that the several laminated layers of the hybrid stack suffer undesired delamination as a result of the deformation process. Thus, the deformation process must be strictly limited, monitored, and controlled, or else such delamination will readily occur.
In another conventional method, it is known to individually preform individual metal sheets using known forming processes, so as to fabricate appropriately shaped individual metal layers having correspondingly formed cross-sections, to be used in the subsequent layering or stacking to form a finished profile member. Namely, once all of the individual metal layers have been formed as needed, they are then stacked and laminated together by the adhesive bonding provided by the binder material as it is cured and hardened, in order to obtain the finished profile member construction in the pre-formed configuration. In such a method, each individual layer requires its own individualized contour. Namely, to avoid layer thickness variations, different curvature developments and forming characteristics of the several individual layers must be taken into account. This leads to rather high tooling costs, fabrication effort, and fabrication costs. Also, such a method is only able to achieve contoured profiles having relatively large radii of curvature, similarly to the above described method.
In view of the above, it is an object of the invention to provide a method of fabricating a profile member of a hybrid composite material including metal layers and at least one fiber-reinforced composite layer, whereby the finished profile member can be fabricated in substantially any desired form, contour or configuration, without being limited to relatively large radii of curvature. It is a further object of the invention to provide such a member, whereby the forming process results directly in a substantially finished profile member, without requiring any after-machining or post-processing such as complex and costly straightening, bending or orienting of the fabricated profile member. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a method of manufacturing a profile member of a hybrid composite material including metal layers and at least one fiber-reinforced composite layer.
In a first step of the method, the individual metal and fiber-reinforced composite layers are alternately stacked, while the composite layers are still wet with a thermally curable resin or other binder, so that this binder wets and adheres to the surfaces of the metal layers, so as to form thereof an uncured initial layer structure. Preferably, each composite layer is a prepreg of a fiber-reinforced composite material such as a carbon fiber composite, a graphite fiber composite, a glass fiber composite, or an aramid fiber composite, which is impregnated with a suitable curable binder. Preferably, the laminated stack of metal and composite layers is formed in the first step to have a flat planar configuration. In other words, all of the layers respectively extend along flat planes parallel to each other.
In a second step of the method, the laminated stack, i.e. the initial uncured layer structure, is plastically deformed in successive deforming steps by means of pressure or bending deformation to the required extent until the initial laminated stack has its cross-section deformed into a predefined profile shape or prescribed cross-sectional contour that differs from the initial cross-sectional contour of the initial layer structure. With this invention radii from 2 mm-10 mm are feasible.
In a third step of the inventive method, the formed laminated stack or deformed layer structure, which has been deformed into the predefined profile shape in the preceding step, is then placed and positioned in an autoclave and subjected to pressure and heat in order to cure and harden the binder of the composite material layers. Thereby, the finished profile member having the finished profile shape is achieved.